Page 78 - University of Pretoria RESEARCH REVIEW 2016
P. 78

 NATURAL environments
 It hasn’t rained in the central Namib Desert since 2011, and there is little visual evidence of life on the desert surface.
Despite the extreme nature of the desert soil habitat,
Professor Don Cowan and his research team at the
Centre for Microbial Ecology and Genomics (CMEG)
have demonstrated that the microbial populations
in these arid soils are alive and well. The group has
been asking fundamental questions of the nature of
desert soil microbial community structures, functions
and adaptations. The latter has led to their recent
publication, in Nature Reviews Microbiology, of a comprehensive review of the molecular adaptations used by bacteria to survive desiccation.
Professor Cowan and the CMEG researchers use a suite of modern molecular phylogenetic and metagenomics technologies, heavily based on the use of Next Generation nucleic acid sequencing and complex bioinformatics programmes and pipelines. He notes that CMEG researchers have been able to determine the true diversity of all important desert soil microbial taxa – bacteria, fungi, archaea and even their viruses. The use of complete metagenome sequencing has provided detailed information on the genetic potential of these community members: the genes involved in stress-responses, the pathways for nitrogen and carbon turnover, the genetic capacity of degradation of xenobiotic compounds, and much more.
CMEG researchers have used a wide range of different desert habitats, gradients and transects in their studies. Their early studies focused on the unusual water gradient across the 200 km breadth of the Namib Desert, where the western coastal zone receives frequent fog water input but almost no rain; the eastern mountain zone receives regular seasonal rainfall; and the central hyper-arid zone receives little of either! This natural gradient provides a near-unique system to investigate the nature and extent of water input on desert soil ecology.
In their latest field experiments, CMEG researchers have shifted their focus from microbial community structure to microbial community functions and responses. A year- long survey of microbial community composition showed that community structures were relatively static, but responded rapidly to the one brief shower of rain, with a rapid increase in the dominance of the cyanobacteria, the keystone taxa in desert soils. A short- timescale experiment, with soil samples recovered at eight-hourly intervals over just four days, showed that community functional responses were remarkably adaptable. These findings are important in terms of understanding how desert soil microbes may respond and adapt to the effects of future climate change.
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